The present invention relates to an improved retainer type lead-acid battery in which the electrolyte is impregnated and retained in the positive and negative active materials of the battery and in a porous separator, and which has no flooded electrolyte present.
Retainer type lead-acid batteries generally have poor high discharge rate performance at low temperatures in comparison with ordinary lead-acid batteries that have a sufficient supply of freely fluid electrolyte. In order to achieve high rate discharge satisfactorily, sulfate ions or hydrogen ions must quickly diffuse from the electrolyte into microscopic pores in the electrode plates. This requirement is satisfied fairly easily by ordinary lead-acid batteries having an ample supply of fluid electrolyte, but in the retainer type lead-acid batteries in which the electrolyte is impregnated and retained only in the positive and active materials and in the separator, the diffusion of the electrolyte to the electrode plates during discharge is so slow that a decrease in the battery's capacity often occurs.
The reason for this is as follows: The separator, which is made of very fine glass fibers and which has a high affinity for the electrolyte, has a porosity of no smaller than 90%, but on the other hand, the positive and negative materials have porosities of only 40 to 50% and their affinity for the electrolyte is fairly low, causing the electrolyte to be predominantly present in the separator. Additionally, no flooded electrolyte is present between the electrodes and the separator, increasing the chance of the occurrence of a gap therebetween, which gap retards the transport of the electrolyte from the separator to either electrode plate. This problem is particularly serious at the positive electrode plate where water formed during discharge (in accordance with the following reaction) blocks the transfer of sulfate and hydrogen ions: EQU PbO.sub.2 +4H.sup.+ +SO.sub.4.sup.-- +2e.fwdarw.PbSO.sub.4 +2H.sub.2 O.